Effects of Nanoparticles of Metal Oxides on the Survival of the Entomopathogenic Nematode: Steinernema carpocapsae.

Nanoparticles (NPs) are technological engineered materials with unique physical and chemical properties, and dimension of less than 100 nm. Nanotechnology has developed at a rapid pace, resulting into tremendous wide application that has resulted into concerns and ecotoxicological consequences. The antimicrobial potentials of the nanoparticles have been extensively studied, however, little has been done on the allied health and environmental toxicity assessments. Thus, the current work evaluated the toxicity effects of the ZnO, TiO2 and Fe3O4 NPs on the survival of the entomopathogenic nematodes (Steinernema carpocapsae), as well as their growth inhibition effects on the nematode symbiotic bacteria (Xenorhabdus nematophila). The metal oxides NPs were characterized by scanning electron microscope and transmission electron microscope. Their toxicity effects were evaluated at various concentrations with the consideration of the media on the toxicity influence. All metal oxides had less influence on the survival of the entomopathogenic nematode and growth of the nematode symbiotic bacterial partner in a concentration dependant manner NPs. The observed toxicity was in the order of Fe3O4 < TiO2 < ZnO NPs respectively, with no significant difference between the NPs. The less toxic effect of the NPs noted may be associated with the ability of entomopathogenic nematodes and their bacterial partner to tolerate toxicants. Nonetheless, other toxicity parameter of NPs on the beneficial nematodes needs to be evaluated for consideration of the compatibility potential of the nematodes and NPs for pest management.

Influence of Metal Oxides Nanoparticles on Pathogenicity of Steinernema carpocapsae Nematodes Against Lepidopteran Galleria mellonella.

Entomopathogenic nematodes (EPNs) have been cited as a safe and effective method for pest management. Their virulence against lepidopterans and other foliar pest has been demonstrated in the laboratory, but achieving field efficacy is challenged with environmental conditions such as desiccation and ultraviolet radiations. Nanoparticles (NPs) as UV-blocking agents have been reported to provide an alternative approach to enhance the EPNs efficacy. We screened the effect of ZnO, TiO2 and Fe3O4 NPs on survival and pathogenicity of EPNs, and determined whether the nanoparticles could provide protection to the EPNs at low concentrations when applied in direct sunlight. All nanoparticles had less influence on the survival of infective juveniles and did not deprive their pathogenic properties following prolonged exposure. The survival rate of nematodes decreased with increased concentrations, with no measurable difference between NPs. Moreover, the survival rate of nematodes exposed to UV radiation in different formulation decreased significantly with the increase in exposure time (p < 0.001). On the other side when EPNs in nanoparticles formulations were exposed to sunlight, their efficacy significantly improved by protecting nematodes from ultraviolet radiation when compared to the water-based formulation. Pathogenic efficacy after exposure to sunlight was in the order of ZnO > TiO2 > Fe3O4 > H2O, indicating the compatibility of nematodes and NPs, and the benefit of different NPs in EPNs formulations. General nanoparticles are novel ingredients that provide suitable protection of EPNs for management of foliar pests. However, the EPNs nanoparticles formulation under a specific agricultural system and climatic condition need to be established.

Larvicidal activity of Hypoestes forskaolii (Vahl) R. Br root extracts against Anopheles gambiae Giless.s, Aedes aegypti L, and Culex quinquefasciatus Say.

Aim: This study aimed to evaluate larvicidal activity of Hypoestes forskaolii R. Br root extract against 3rd instar Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus. Methods: A protocol developed by the World Health Organization was adopted, with minor modification using chloroform and methanol extracts with concentrations ranging from 25-750 µg/mL. Results: The H. forskaolii chloroform extract exhibited very high larvicidal activity after 72 hours of exposure, with LC50 2.0322, 3.8989, 6.0004 µg/mL against A. gambiae, A. aegypti, and C. quinquefasciatus, respectively. Conclusion: The larvicidal activity of H. forskaolii is reported for the first time in this paper. The effectiveness of H. forskaolii chloroform extract warrants further research to develop botanical mosquito repellants from this source.